diff --git a/app/scripts/background.js b/app/scripts/background.js
index 736e60603202..0d6f1c97c0ae 100644
--- a/app/scripts/background.js
+++ b/app/scripts/background.js
@@ -47,7 +47,7 @@ import rawFirstTimeState from './first-time-state';
 import getFirstPreferredLangCode from './lib/get-first-preferred-lang-code';
 import getObjStructure from './lib/getObjStructure';
 import setupEnsIpfsResolver from './lib/ens-ipfs/setup';
-import { getPlatform } from './lib/util';
+import { deferredPromise, getPlatform } from './lib/util';
 /* eslint-enable import/first */
 
 const { sentry } = global;
@@ -94,16 +94,17 @@ const ACK_KEEP_ALIVE_MESSAGE = 'ACK_KEEP_ALIVE_MESSAGE';
 const WORKER_KEEP_ALIVE_MESSAGE = 'WORKER_KEEP_ALIVE_MESSAGE';
 
 /**
- * In case of MV3 we attach a "onConnect" event listener as soon as the application is initialised.
- * Reason is that in case of MV3 a delay in doing this was resulting in missing first connect event after service worker is re-activated.
+ * This deferred Promise is used to track whether initialization has finished.
  *
- * @param remotePort
+ * It is very important to ensure that `resolveInitialization` is *always*
+ * called once initialization has completed, and that `rejectInitialization` is
+ * called if initialization fails in an unrecoverable way.
  */
-const initApp = async (remotePort) => {
-  browser.runtime.onConnect.removeListener(initApp);
-  await initialize(remotePort);
-  log.info('MetaMask initialization complete.');
-};
+const {
+  promise: isInitialized,
+  resolve: resolveInitialization,
+  reject: rejectInitialization,
+} = deferredPromise();
 
 /**
  * Sends a message to the dapp(s) content script to signal it can connect to MetaMask background as
@@ -154,13 +155,26 @@ const sendReadyMessageToTabs = async () => {
   }
 };
 
-if (isManifestV3) {
-  browser.runtime.onConnect.addListener(initApp);
-  sendReadyMessageToTabs();
-} else {
-  // initialization flow
-  initialize().catch(log.error);
-}
+// These are set after initialization
+let connectRemote;
+let connectExternal;
+
+browser.runtime.onConnect.addListener(async (...args) => {
+  // Queue up connection attempts here, waiting until after initialization
+  await isInitialized;
+
+  // This is set in `setupController`, which is called as part of initialization
+  connectRemote(...args);
+});
+browser.runtime.onConnectExternal.addListener(async (...args) => {
+  // Queue up connection attempts here, waiting until after initialization
+  await isInitialized;
+
+  // This is set in `setupController`, which is called as part of initialization
+  connectExternal(...args);
+});
+
+initialize().catch(log.error);
 
 /**
  * @typedef {import('../../shared/constants/transaction').TransactionMeta} TransactionMeta
@@ -220,17 +234,22 @@ if (isManifestV3) {
 /**
  * Initializes the MetaMask controller, and sets up all platform configuration.
  *
- * @param {string} remotePort - remote application port connecting to extension.
  * @returns {Promise} Setup complete.
  */
-async function initialize(remotePort) {
-  const initState = await loadStateFromPersistence();
-  const initLangCode = await getFirstPreferredLangCode();
-  setupController(initState, initLangCode, remotePort);
-  if (!isManifestV3) {
-    await loadPhishingWarningPage();
+async function initialize() {
+  try {
+    const initState = await loadStateFromPersistence();
+    const initLangCode = await getFirstPreferredLangCode();
+    setupController(initState, initLangCode);
+    if (!isManifestV3) {
+      await loadPhishingWarningPage();
+    }
+    await sendReadyMessageToTabs();
+    log.info('MetaMask initialization complete.');
+    resolveInitialization();
+  } catch (error) {
+    rejectInitialization(error);
   }
-  log.info('MetaMask initialization complete.');
 }
 
 /**
@@ -362,9 +381,8 @@ async function loadStateFromPersistence() {
  *
  * @param {object} initState - The initial state to start the controller with, matches the state that is emitted from the controller.
  * @param {string} initLangCode - The region code for the language preferred by the current user.
- * @param {string} remoteSourcePort - remote application port connecting to extension.
  */
-function setupController(initState, initLangCode, remoteSourcePort) {
+function setupController(initState, initLangCode) {
   //
   // MetaMask Controller
   //
@@ -413,16 +431,6 @@ function setupController(initState, initLangCode, remoteSourcePort) {
 
   setupSentryGetStateGlobal(controller);
 
-  //
-  // connect to other contexts
-  //
-  if (isManifestV3 && remoteSourcePort) {
-    connectRemote(remoteSourcePort);
-  }
-
-  browser.runtime.onConnect.addListener(connectRemote);
-  browser.runtime.onConnectExternal.addListener(connectExternal);
-
   const isClientOpenStatus = () => {
     return (
       popupIsOpen ||
@@ -463,7 +471,7 @@ function setupController(initState, initLangCode, remoteSourcePort) {
    *
    * @param {Port} remotePort - The port provided by a new context.
    */
-  function connectRemote(remotePort) {
+  connectRemote = async (remotePort) => {
     const processName = remotePort.name;
 
     if (metamaskBlockedPorts.includes(remotePort.name)) {
@@ -566,16 +574,16 @@ function setupController(initState, initLangCode, remoteSourcePort) {
       }
       connectExternal(remotePort);
     }
-  }
+  };
 
   // communication with page or other extension
-  function connectExternal(remotePort) {
+  connectExternal = (remotePort) => {
     const portStream = new PortStream(remotePort);
     controller.setupUntrustedCommunication({
       connectionStream: portStream,
       sender: remotePort.sender,
     });
-  }
+  };
 
   //
   // User Interface setup
diff --git a/app/scripts/lib/util.js b/app/scripts/lib/util.js
index 58c0b3c89687..929b5d60219a 100644
--- a/app/scripts/lib/util.js
+++ b/app/scripts/lib/util.js
@@ -191,3 +191,30 @@ export const generateRandomId = () => {
 export const isValidDate = (d) => {
   return d instanceof Date && !isNaN(d);
 };
+
+/**
+ * A deferred Promise.
+ *
+ * A deferred Promise is one that can be resolved or rejected independently of
+ * the Promise construction.
+ *
+ * @typedef {object} DeferredPromise
+ * @property {Promise} promise - The Promise that has been deferred.
+ * @property {() => void} resolve - A function that resolves the Promise.
+ * @property {() => void} reject - A function that rejects the Promise.
+ */
+
+/**
+ * Create a defered Promise.
+ *
+ * @returns {DeferredPromise} A deferred Promise.
+ */
+export function deferredPromise() {
+  let resolve;
+  let reject;
+  const promise = new Promise((innerResolve, innerReject) => {
+    resolve = innerResolve;
+    reject = innerReject;
+  });
+  return { promise, resolve, reject };
+}
diff --git a/app/scripts/lib/util.test.js b/app/scripts/lib/util.test.js
index 0892a4e3dea6..a4c5d7b5f030 100644
--- a/app/scripts/lib/util.test.js
+++ b/app/scripts/lib/util.test.js
@@ -9,7 +9,7 @@ import {
   PLATFORM_CHROME,
   PLATFORM_EDGE,
 } from '../../../shared/constants/app';
-import { getEnvironmentType, getPlatform } from './util';
+import { deferredPromise, getEnvironmentType, getPlatform } from './util';
 
 describe('app utils', () => {
   describe('getEnvironmentType', () => {
@@ -154,4 +154,58 @@ describe('app utils', () => {
       expect(getPlatform()).toStrictEqual(PLATFORM_CHROME);
     });
   });
+
+  describe('deferredPromise', () => {
+    it('should allow rejecting a deferred Promise', async () => {
+      const { promise, reject } = deferredPromise();
+
+      reject(new Error('test'));
+
+      await expect(promise).rejects.toThrow('test');
+    });
+
+    it('should allow resolving a deferred Promise', async () => {
+      const { promise, resolve } = deferredPromise();
+
+      resolve('test');
+
+      await expect(promise).resolves.toBe('test');
+    });
+
+    it('should still be rejected after reject is called twice', async () => {
+      const { promise, reject } = deferredPromise();
+
+      reject(new Error('test'));
+      reject(new Error('different message'));
+
+      await expect(promise).rejects.toThrow('test');
+    });
+
+    it('should still be rejected after resolve is called post-rejection', async () => {
+      const { promise, resolve, reject } = deferredPromise();
+
+      reject(new Error('test'));
+      resolve('different message');
+
+      await expect(promise).rejects.toThrow('test');
+    });
+
+    it('should still be resolved after resolve is called twice', async () => {
+      const { promise, resolve } = deferredPromise();
+
+      resolve('test');
+      resolve('different message');
+
+      await expect(promise).resolves.toBe('test');
+    });
+
+    it('should still be resolved after reject is called post-resolution', async () => {
+      const { promise, resolve, reject } = deferredPromise();
+
+      resolve('test');
+      reject(new Error('different message'));
+
+      await expect(promise).resolves.toBe('test');
+    });
+  });
 });
diff --git a/app/scripts/metamask-controller.test.js b/app/scripts/metamask-controller.test.js
index b2aaf665f805..232e985505c4 100644
--- a/app/scripts/metamask-controller.test.js
+++ b/app/scripts/metamask-controller.test.js
@@ -12,7 +12,7 @@ import createTxMeta from '../../test/lib/createTxMeta';
 import { NETWORK_TYPES } from '../../shared/constants/network';
 import { KEYRING_TYPES } from '../../shared/constants/keyrings';
 import { DEVICE_NAMES } from '../../shared/constants/hardware-wallets';
-import { addHexPrefix } from './lib/util';
+import { addHexPrefix, deferredPromise } from './lib/util';
 
 const Ganache = require('../../test/e2e/ganache');
 
@@ -1238,11 +1238,3 @@ describe('MetaMaskController', function () {
     });
   });
 });
-
-function deferredPromise() {
-  let resolve;
-  const promise = new Promise((_resolve) => {
-    resolve = _resolve;
-  });
-  return { promise, resolve };
-}